Inflation, Symmetry, and B-Modes

We examine the role of using symmetry and effective field theory in inflationary model building. We describe the standard formulation of starting with an approximate shift symmetry for a scalar field, and then introducing corrections systematically in order to maintain control over the inflationary potential. We find that this leads to models in good agreement with recent data. 

On the other hand, there are attempts in the literature to deviate from this paradigm by envoking other symmetries and corrections. In particular: in a suite of recent papers, several authors have made the claim that standard Einstein gravity with a cosmological constant and a massless scalar carries conformal symmetry. They further claim that such a theory carries another hidden symmetry; a global SO(1,1) symmetry. By deforming around the global SO(1,1) symmetry, they are able to produce a range of inflationary models with asymptotically flat potentials, whose flatness is claimed to be protected by these symmetries. 

Image : alice.loria.fr

These models tend to give rise to B-modes with small amplitude. Here we explain that these authors are merely introducing a redundancy into the description, not an actual conformal symmetry. Furthermore, we explain that the only real (global) symmetry in these models is not at all hidden, but is completely manifest when expressed in the Einstein frame; it is in fact the shift symmetry of a scalar field. When analyzed systematically as an effective field theory, deformations do not generally produce asymptotically flat potentials and small B-modes, but other types of potentials with B-modes of large amplitude; nicely compatible with recent BICEP2 data. Such simple models typically also produce the observed red spectral index, Gaussian fluctuations, etc. In short: simple models of inflation, organized by expanding around a shift symmetry, are in excellent agreement with recent data.

Link : http://arxiv.org/pdf/1403.5253

Claim New Study, Every Blackhole is a Portal to Another Universe

A black hole is a region of spacetime from which gravity prevents anything, including light, from escaping. The theory of general relativity predicts that a sufficiently compact mass will usually deform spacetime to form a black hole. Around a black hole, there is a mathematically defined surface called an event horizon that marks the point of no return.  [wikipedia]

The new theory was developed by Jorge Pullin of the State University of Louisiana and Rodolfo Gambino of the University of the Republic of Uruguay. The two scientists decided to study the predictions of the theory of quantum gravity in black holes. More specifically, they applied the equations of quantum gravity in a non-rotating black hole with spherical symmetry.

As described in other theories, as the matter approaches the core of the black hole, the gravitational field becomes more and more powerful, but it does not disappear into a spacetime singularity as the prevailing theory states. According to the study results of the two researchers, the matter does not disappear in the middle of the hole but continues its way up the other end and into another universe. “Like part of a cosmic Russian doll, our universe may be nested inside a black hole that is itself part of a larger universe.

image: http://www.shutterstock.com/pic.mhtml?id=25016035

In turn, all the black holes found so far in our universe—from the microscopic to the supermassive—may be doorways into alternate realities.” According to the new equations, the matter black holes absorb and seemingly destroy is actually expelled and becomes the building blocks for galaxies, stars, and planets in another reality. Essentially, every black hole contains a smaller alternate universe. And our universe might just exist inside a black hole of a galaxy in a much larger universe. So within the 100 billion galaxies in our known universe lies 100 billion universes in the galactic black holes of our universe, with 100 billion more galaxies each containing another universe with more galaxies, and so on infinitely.

The new model isn't the first to propose that other universes exist inside black holes. Damien Easson, a theoretical physicist at Arizona State University, has made the speculation in previous studies. “What is new here is an actual wormhole solution in general relativity that acts as the passage from the exterior black hole to the new interior universe,” said Easson, who was not involved in the new study. So the idea that black holes are portals to other worlds rather than a place of absolute destruction is not new. But they all stumbled on the spacetime singularity.

This is the first time when this barrier is bypassed with the help of scientific tools. The results of the study were published in the journal Physical Review Letters. Furthermore, a recent study published in the scientific journal Nature shows that our entire universe may have been born out of a black hole from another universe. In other words, the Big Bang was really just an extension of a black hole in a different universe.

Source : http://www.whydontyoutrythis.com/2014/03/every-black-hole-contains-another-universe-claims-new-study.html

Discovery of Large Scale Tensor Mode and Chaotic Inflation in Supergravity

SUGRA, or SUper GRAvity, was discovered in 1976 by Dan Freedman, Sergio Ferrara and Peter Van Nieuwenhuizen. In theoretical physics, supergravity (supergravity theory) is a field theory that combines the principles of supersymmetry and general relativity. Together, these imply that, in supergravity, the supersymmetry is a local symmetry (in contrast to non-gravitational supersymmetric theories, such as the Minimal Supersymmetric Standard Model). Since the generators of supersymmetry (SUSY) are convoluted with the Poincaré group to form a super-Poincaré algebra, it can be seen that supergravity follows naturally from supersymmetry.

Like any field theory of gravity, a supergravity theory contains a spin-2 field whose quantum is the graviton. Supersymmetry requires the graviton field to have a superpartner. This field has spin 3/2 and its quantum is the gravitino. The number of gravitino fields is equal to the number of supersymmetries.

The BICEP2 collaboration has recently reported a large tensor fluctuation in the cosmic microwave background, which suggests chaotic inflation models. In this letter, we reconsider the chaotic inflation model in the supergravity. We introduce a non-holomorphic shift-symmetry breaking parameter, which we expect to exist in general, and discuss its effect on the inflaton dynamics. We show that the model predicts a sizable deviation from the original chaotic inflation model and the predicted tensor fluctuation can lie between the BICEP2 result and the upper bound given by the Planck experiment with a small shift-symmetry breaking parameter. The model is characterized by only two parameters, which yields predictability and testability in future experiments.

Cosmic inflation is a natural scenario which not only solves the flatness and the horizon problem, but also explains the large scale structure of the universe and the fluctuation of the cosmic microwave background (CMB) radiation. Precise observations of the CMB begins to reveal nature of inflation. Chaotic inflation models have been studied in the literature, especially in the context of the supergravity theory (SUGRA). In this letter, we reconsider chaotic in ation models in the SUGRA...

Read more : http://en.wikipedia.org/wiki/Supergravity || http://arxiv.org/pdf/1403.4729

The Limits of Gauge-Gravity Duality

by Brett McInnes

In quantum field theory, gauge gravitation theory is the effort to extend Yang–Mills theory, which provides a universal description of the fundamental interactions, to describe gravity. It should not be confused with the related but distinct gauge theory gravity.

The first gauge model of gravity was suggested by R. Utiyama in 1956 just two years after birth of the gauge theory itself, However, the initial attempts to construct the gauge theory of gravity by analogy with the gauge models of internal symmetries encountered a problem of treating general covariant transformations and establishing the gauge status of a pseudo-Riemannian metric (a tetrad field).

The Quark-Gluon Plasma [QGP] is described in terms of gauge-gravity duality by charged, locally asymptotically AdS black holes. This duality cannot however be expected to account for an arbitrarily large domain in the quark-matter phase diagram: one does not for example expect that it will provide a good description at extremely high temperatures [where a fully "stringy" account of the bulk will be necessary]. We argue that, likewise, the gauge-gravity duality itself points to a bound on its applicability in the direction of large chemical potentials, though in most cases at values far beyond experimental access. However, the upper bound can, in some circumstances, depend strongly on the amount of angular momentum present, and it is conceivable that this bound could be probed by experiments designed to produce rapidly rotating quark-gluon plasmas with large chemical potentials.

Read more : http://en.wikipedia.org/wiki/Gauge_gravitation_theory ||http://arxiv.org/pdf/1403.3258

Breaking News : First Direct Evidence of Cosmic Inflation

via : cfa.harvard,edu

Researchers from the BICEP2 collaboration today announced the first direct evidence for this cosmic inflation. Their data also represent the first images of gravitational waves, or ripples in space-time. These waves have been described as the "first tremors of the Big Bang." Finally, the data confirm a deep connection between quantum mechanics and general relativity.

"Detecting this signal is one of the most important goals in cosmology today. A lot of work by a lot of people has led up to this point," said John Kovac (Harvard-Smithsonian Center for Astrophysics), leader of the BICEP2 collaboration.

These groundbreaking results came from observations by the BICEP2 telescope of the cosmic microwave background -- a faint glow left over from the Big Bang. Tiny fluctuations in this afterglow provide clues to conditions in the early universe. For example, small differences in temperature across the sky show where parts of the universe were denser, eventually condensing into galaxies and galactic clusters.

Since the cosmic microwave background is a form of light, it exhibits all the properties of light, including polarization. On Earth, sunlight is scattered by the atmosphere and becomes polarized, which is why polarized sunglasses help reduce glare. In space, the cosmic microwave background was scattered by atoms and electrons and became polarized too.

"Our team hunted for a special type of polarization called 'B-modes,' which represents a twisting or 'curl' pattern in the polarized orientations of the ancient light," said co-leader Jamie Bock (Caltech/JPL).

Gravitational waves squeeze space as they travel, and this squeezing produces a distinct pattern in the cosmic microwave background. Gravitational waves have a "handedness," much like light waves, and can have left- and right-handed polarizations.

"The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky," said co-leader Chao-Lin Kuo (Stanford/SLAC).

The team examined spatial scales on the sky spanning about one to five degrees (two to ten times the width of the full Moon). To do this, they traveled to the South Pole to take advantage of its cold, dry, stable air.

"The South Pole is the closest you can get to space and still be on the ground," said Kovac. "It's one of the driest and clearest locations on Earth, perfect for observing the faint microwaves from the Big Bang."

They were surprised to detect a B-mode polarization signal considerably stronger than many cosmologists expected. The team analyzed their data for more than three years in an effort to rule out any errors. They also considered whether dust in our galaxy could produce the observed pattern, but the data suggest this is highly unlikely.

"This has been like looking for a needle in a haystack, but instead we found a crowbar," said co-leader Clem Pryke (University of Minnesota).

When asked to comment on the implications of this discovery, Harvard theorist Avi Loeb said, "This work offers new insights into some of our most basic questions: Why do we exist? How did the universe begin? These results are not only a smoking gun for inflation, they also tell us when inflation took place and how powerful the process was."

BICEP2 is the second stage of a coordinated program, the BICEP and Keck Array experiments, which has a co-PI structure. The four PIs are John Kovac (Harvard), Clem Pryke (UMN), Jamie Bock (Caltech/JPL), and Chao-Lin Kuo (Stanford/SLAC). All have worked together on the present result, along with talented teams of students and scientists. Other major collaborating institutions for BICEP2 include the University of California at San Diego, the University of British Columbia, the National Institute of Standards and Technology, the University of Toronto, Cardiff University, Commissariat à l'Energie Atomique.

BICEP2 is funded by the National Science Foundation (NSF). NSF also runs the South Pole Station where BICEP2 and the other telescopes used in this work are located. The Keck Foundation also contributed major funding for the construction of the team’s telescopes. NASA, JPL, and the Moore Foundation generously supported the development of the ultra-sensitive detector arrays that made these measurements possible.

Technical details and journal papers can be found on the BICEP2 release website:

http://bicepkeck.org

Read more : http://www.cfa.harvard.edu/news/2014-05

Has The First Dark Matter Particle Been Found?

via : I Fuck Love Science by Stephen Luntz

The existence of dark matter has been known for decades, but working out what it is actually made from has been a frustrating quest. Now, however, Professor David Cline has told a UCLA symposium of the finding of what could be the first cold dark matter particle, an object weighing 30 billion electron volts.

The first evidence for dark matter emerged in 1932 when Jan Oort noted that objects are circling the galactic plane as if our galaxy has substantially more mass than we can see. Further study on other galaxies found the same pattern. Two main theories emerged: Weakly Interacting Massive Particles (WIMPS) or Massive Compact Halo Objects (MACHOs). The first involves subatomic particles with no electromagnetic charge or strong nuclear interaction; the second posits objects the size of planets or stars that don't shine.

The problem is far from trivial. It is estimated that the dark matter we cannot see accounts for more than five times as much mass in the universe as the ordinary matter we can. Over time the weight of scientific support has shifted to the idea that WIMPS account for most of what we are missing, but finding them has been more of a problem. Neutrinos were thought to be the answer, but the neutrinos left over from the formation of the universe travel too fast, and so would be too evenly spread, to account for the mass clumped around galaxies.

What is needed is “cold dark matter” particles, ones that travel slowly enough that those produced in the big bang would have clumped together in the spots that became modern day galaxies.

Every two years UCLA convenes a symposium to discuss progress in the search for dark matter of one form or another. Nothing has yet been published, but Cline, of the home campus's College of Letters and Science, commented, "At this symposium, it was obvious that excitement is building in the fields of dark matter theory and, especially, detection."

The Fermi telescope has found mysterious gamma rays, which Cline thinks may be emitted by the particles. Attempts to get WIMPs to interact with atomic nuclei in underground laboratories have failed to find anything, but Cline said, "there is no incompatibility [in these detectors' null results] with the interesting excess in the FERMI data."

Subatomic particles are classified by their mass, but by the famous E=mc2 mass can be converted to energy, making electron volts, a unit of energy, often the favored way to describe them. For comparison, protons have a mass of just under a billion electron volts.

"Because dark matter makes up the bulk of the mass of galaxies and is fundamental in the formation of galaxies and stars, it is essential to the origin of life in the universe and on Earth," said Cline.

Read more at http://www.iflscience.com/physics/has-first-dark-matter-particle-been-found#7W7MLRMHgZScVm1h.99

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In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. In string theory, the different types of observed elementary particles arise from the different quantum states of these strings. In addition to the types of particles postulated by the standard model of particle physics, string theory naturally incorporates gravity, and is therefore a candidate for a theory of everything, a self-contained mathematical model that describes all fundamental forces and forms of matter. Aside from this hypothesized role in particle physics, string theory is now widely used as a theoretical tool in physics, and it has shed light on many aspects of quantum field theory and quantum gravity. [Wikipedia]

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In particle physics, an elementary particle or fundamental particle is a particle whose substructure is unknown, thus it is unknown whether it is composed of other particles. Known elementary particles include the fundamental fermions (quarks, leptons, antiquarks, and antileptons), which generally are "matter particles" and "antimatter particles", as well as the fundamental bosons (gauge bosons and Higgs boson), which generally are "force particles" that mediate interactions among fermions. A particle containing two or more elementary particles is a composite particle [Wikipedia]

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Gravitational Waves: The Big Bang's Smoking Gun

Gravitational waves are the "smoking gun" of the Big Bang.

via : Space.com

Predicted by Albert Einstein's theory of general relativity in 1916, a massive object like Earth distorts space-time around it like a bowling ball dropped on a trampoline. The larger the object, the more space-time is distorted by it. If a marble were circling around the bowling ball on the dimpled trampoline, it would fall inward, toward the bowling ball, like a rock in space circling a planet. Gravitational waves are ripples in space-time that travel outward from a source.

Scientists think that powerful gravitational waves are created when two extremely dense objects — like a pair of neutron stars or a black hole and a neutron star — orbit one another in binary pairs. The interaction of those two objects swirl space-time, creating ripples that theoretically can be measured using powerful instrumentation

Direct evidence

In 2014, the Harvard-Smithsonian Center for Astrophysics found a faint signal in the cosmic microwave background radiation (CMB) that signifies the first direct evidence of gravitational waves ever discovered. Gravitational waves were the last untested part of Einstein's general theory of relativity.

The Harvard-Smithsonian study spotted gravitational waves as ripples in space-time possible left over from the rapid expansion of the universe (called inflation) right after the Big Bang nearly 13.8 billion years ago.

Scientists working on the study found a distinct curling pattern in the CMB — the comic fog that fills the universe and represents the earliest detectable radiation — that further supports the idea that the universe went through a huge period of inflation a fraction of a second after the Big Bang.

"This work offers new insights into some of our most basic questions: Why do we exist? How did the universe begin?," astrophysicist Avi Loeb, who wasn't a member of the study team said in a statement about the Harvard-Smithsonian research. "These results are not only a smoking gun for inflation, they also tell us when inflation took place and how powerful the process was."

Cosmic inflation

CMB radiation came into existence about 380,000 years after the Big Bang. Scientists have mapped the CMB across the sky and found that it is a uniform temperature, evidence that bolsters cosmic inflation theory.

"Why the cosmic microwave background temperature is the same at different spots in the sky would be a mystery if it was not for inflation saying, well, our whole sky came from this tiny region," Chuck Bennett, principal investigator of NASA's Wilkinson Microwave Anisotropy Probe (WMAP) mission, told Space.com in 2013. "So the idea of inflation helps answer some of these mysteries, and it explains where these fluctuations came from.

New experimentation

Experiments like Advanced LIGO (Laser Interferometer Gravitational Wave Observatory) and Advanced Virgo, could potentially detect those binary-created ripples in space-time, although neither has found a clear signature yet.

"The advanced LIGO detectors that are now being installed will see out through a substantial part of the universe," California Institute of Technology emeritus professor of physics Kip Thorne, a leading proponent of LIGO, said in 2012. "We expect to see black holes colliding at a rate of perhaps somewhere between once an hour and once a year."

Gravitational waves are different from gravity waves, which are ripples created in the atmospheres of planets by the interactions of winds whipping over geological features on the planet's surface.

-Miriam Kramer

The Speed of Darkness

This question, like many others, centers on a negative concept. There are a few of these running around and it is fairly common to get tripped up by them, but part of the fun in science is when you can apply negative concepts to positive ones, helping us better understand how each facet of the universe work together AND independently. One such negative concept asks: “What is darkness?” “And is there such a thing as the speed of darkness?”

QUANTIFYING THE SEEMINGLY IMPOSSIBLE

In order to know what the speed of darkness is, or anything else about it, we would have to quantify it. What is it? Well darkness is the absence of light. So darkness isn’t a thing, it is instead a lack of a thing. Therefore questions about characteristic of darkness, which is an absence instead of a presence, become hard to define.The most correct answer to the question would be that darkness has no speed. In order for something to have speed, it must be able to moverelative to other bodies. Since darkness doesn’t actually exist, it cannot move and therefore cannot have a speed. However, since the level of illumination of a given area cannot change at a different rate than the speed of light, you could also equate it as having the speed of light, though less correctly

A THOUGHT EXPERIMENT

I’ll use an example to make my point. Lets say you are in a room which is completely sealed off from the outside world, and nothing can enter it (particularly light). In this room you have a perfect light bulb. It has no warm up or cool down time, when you flip the switch, it instantly starts or stops producing a steady stream of light. In addition to this, let’s say that the walls do not reflect light, but instead completely absorb it. For convenience, let’s make the room round and have the light bulb at the center. Most of this can’t actually be done, but this is still a helpful thought experiment

Now lets say we suddenly turn off the light bulb. The light will travel at a predictable speed from the bulb, and as it does, it will leave behind it an area without any light at all (meaning the light in the room is receding at the speed of light. Note that the darkness isn’t advancing, but the light is receding. As I’ve said earlier, darkness isn’t actually a thing; therefore, it cannot have a speed.

However the lack of light in our hypothetical room is spreading at the speed of light. Colloquially, this is a minor point. It is however a very important distinction. Darkness doesn’t exist, and therefore cannot spread or move, but light (which obviously does exist) can. And in doing so it can also leave an absence of light, and this absence will grow or shrink at the speed of light.

A SPEED OF DARKNESS IN A NUTSHELL

Since darkness isn’t a tangible thing, it is hard to properly quantify its characteristics. It doesn’t have a speed, but light will always advance or recede at the universal speed limit (186,000 miles per second, or 299,792,458 meters per second)


Source : http://www.fromquarkstoquasars.com/the-speed-of-darkness/

Quantum entanglement in analogue Hawking radiation, when is the final state non-separable ?

Entanglement is a state where the state of two quantum particles (photons, for example) are intrinsically and absolutely linked. Quantum particles, due a principle called quantum superposition, exist in every theoretically possible state at the same time. A photon, for example, spins horizontally and vertically (different polarizations) at the same time. When you measure a quantum particle, though, it fixes on a single state. With entanglement, when you measure one half of the entangled pair, the other half instantly assumes the exact opposite state. If you measure one photon and it’s vertically polarized, its entangled sibling will be horizontally polarized. We study the quantum entanglement of the quasiparticle pairs emitted by analogue black holes. 

We use a phenomenological description of the spectra in dispersive media to study the domains in parameter space where the final state is non-separable. In stationary flows, three modes are involved in each sector of fixed frequency, and not two as in homogeneous situations. The third spectator mode acts as an environment for the pairs, and the strength of the coupling significantly reduces the quantum coherence. The non-separability of the pairs emitted by white holes are also considered, and compared with that of black holes.

One of the main challenges of the analogue gravity program is to conceive and realize experiments where a clear signal of the analogue Hawking effect would be detected. When addressing this question, one should clearly distinguish the induced effect, which purely rests on the dynamics of classical fieelds, i.e., the scattering of incident waves, from the spontaneous effect which arises from the amplication of vacuum fluctuations. However, because the same mode ampli-cation is involved, both channels lead to very similar behaviors. Indeed, the space-time properties of the correlation patterns of the emitted quasi-particles are very much the same whether or not the spontaneous channel signicantly contributed. Therefore, if one wishes to experimentally distinguish the spontaneous from the induced, one must use observables that are sensitive to the small differences between the quantum and the classical.

read more : http://arxiv.org/pdf/1403.3335

Introduce to Loop quantum gravity

Loop quantum gravity (LQG) is a theory that attempts to describe the quantum properties of gravity. It is also a theory of quantum space and quantum time, because, according to general relativity, the geometry of spacetime is a manifestation of gravity. LQG is an attempt to merge and adapt standard quantum mechanics and standard general relativity. The main output of the theory is a physical picture of space where space is granular. The granularity is a direct consequence of the quantization. It has the same nature of the granularity of the photons in the quantum theory ofelectromagnetism or the discrete levels of the energy of the atoms. But here, it is space itself which is discrete.

More precisely, space can be viewed as an extremely fine fabric or network "woven" of finite loops. These networks of loops are called spin networks. The evolution of a spin network over time is called a spin foam. The predicted size of this structure is the Planck length, which is approximately 10−35meters. According to the theory, there is no meaning to distance at scales smaller than the Planck scale. Therefore, LQG predicts that not just matter, but also space itself has an atomic structure.

Today LQG is a vast area of research, developing in several directions, which involves about 50 research groups worldwide.[1] They all share the basic physical assumptions and the mathematical description of quantum space. The full development of the theory is being pursued in two directions: the more traditional canonical loop quantum gravity, and the newer covariant loop quantum gravity, more commonly called spin foam theory.

Research into the physical consequences of the theory is proceeding in several directions. Among these, the most well-developed is the application of LQG to cosmology, called Loop quantum cosmology (LQC). LQC applies LQG ideas to the study of the early universe and the physics of the Big Bang. Its most spectacular consequence is that the evolution of the universe can be continued beyond the Big Bang. The Big Bang appears thus to be replaced by a sort of cosmic Big Bounce.

 

Loop quantum gravity is string theory’s biggest competitor. It gets less press than string theory, in part because it has a fundamentally more limited goal: a quantum theory of gravity. Loop quantum gravity performs this feat by trying to quantize space itself — in other words, treat space like it comes in small chunks.

In contrast, string theory starts with methods of particle physics and frequently hopes to not only provide a method of creating a quantum theory of gravity, but also explain all of particle physics, unifying gravity with the other forces at the same time. Oh, and it predicts extra dimensions, which is very cool!

source : http://en.wikipedia.org/wiki/Loop_quantum_gravity ; www.dummies.com/how-to/content/string-theory-and-loop-quantum-gravity.html

A Quantum Bound State Description of Black Holes

Black holes are embedded as bound states in a relativistic quantum theory of weakly coupled constituent fields. The constituents are immersed in a non perturbative vacuum structure representing strong collective effects via in medium modifications. The latter are parametrized in terms of condensates. Observables such as the constituent distribution, the constituent number and energy density are constructed, and calculated at the parton level. Remarkably, even at this level, these observables receive only non perturbative contributions. Furthermore, observables associated with the interior of black holes show simple scalings with the total constituent number. Finally, an explicit framework for calculating gauge corrections is presented.

Qualifying the importance of space{time geometry relative to the fundamental status of Hilbert{space geometry gives rise to a prominent cultural clash across physics communities. The favoured perspective seems to prefer quantum mechanics as the sole fundamental framework, while space{time geometry appears to be a derived rather than a basic concept. The combination of quantum mechanics with causal structures, however, requires light{ cones at its foundation. This potential tension is resolved by distinguishing the Minkowski light{cone in accordance with locality principles. Within this framework, general relativity is an e ffective description derived from an underlying quantum theory of the gravitational eld. As such its domain of validity is, a priori, restricted to deformations of the fundamental Minkowski light cone. Beyond this domain, solutions of general relativity are either describing new ground states, thus qualifying the existence of a fundamental light{cone, or, in accordance with a distinguished causal structure, are mere geometrical artefacts void of a Hilbert space connection.

In this article, we follow a more pragmatic approach and show how certain space{times can be, at least complementary, described as quantum bound states. The bound state description is explicitly developed in the case of Schwarzschild black holes. This example is particularly plausible since it admits a distinct spherical surface that is of fundamental signi cance. On the near side of the Schwarzschild surface, the causal structure is granted by light{cones that can be described as weakly deformed cousins of Minkowski light{cones. At the Schwarzschild surface, however, these deformations become strong. Accordingly, the interior of the Schwarzschild sphere might not be represented by a physical geometry, albeit a geometrical solution exists. The relation of this geometrical solution to quantum mechanics is unclear and it is doubtful that one can be established. Therefore, in the present work, it will be quali ed as unphysical. As a consequence, the geometrical de nition of a black hole is valid only on the near side of the Schwarzschild surface. Clearly, this de nition cannot be fundamental.

In summary, the Schwarzschild surface can be considered as a boundary separating the interior of a quantum bound state from an exterior admitting an approximate geometrical description.

Read more : http://arxiv.org/pdf/1403.3224